A guanidine derivative having an insecticidal activity and a method for producing the same are disclosed in JP-A-157308/1991. As an improved method for producing the guanidine derivative, a method for producing via an isourea derivative is disclosed in WO97/00867 as shown in the following scheme 1. ##STR4##
wherein R.sub.1 and R.sub.2 are the same or different, and each represents a hydrogen atom or an optionally substituted hydrocarbon group; R.sub.3 represents an optionally substituted amino group; A represents a divalent hydrocarbon group which may optionally be substituted; Q' represents an optionally substituted heterocyclic group; X represents an electron withdrawing group; Y.sub.1 and Y.sub.2 are the same or different, and each represents a leaving group; and n represents 0 or 1. PA1 wherein R.sup.1 represents an optionally substituted hydrocarbon group; R.sup.2 represents a hydrogen atom or an optionally substituted hydrocarbon group; and Q represents an optionally substituted heterocyclic group, or a salt thereof can be produced in a high yield by subjecting a compound represented by the formula: ##STR7## PA1 wherein R.sup.1 has the same meaning as defined above, or a salt thereof to a nitration reaction (a), and further subjecting the resulting mixture without isolating/purifying the resulting compound represented by the formula: ##STR8## PA1 wherein R.sup.1 has the same meaning as defined above, or a salt thereof to a reaction (b) with a compound represented by the formula: EQU Q--CH.sub.2 --NH--R.sup.2 [III] PA1 wherein each symbol has the same meaning as defined above, or a salt thereof. PA1 wherein R.sup.1 represents an optionally substituted hydrocarbon group; R.sup.2 represents a hydrogen atom or an optionally substituted hydrocarbon group; and Q represents an optionally substituted heterocyclic group, or a salt thereof which comprises subjecting a compound represented by the formula: ##STR10## PA1 wherein R.sup.1 has the same meaning as defined above, or a salt thereof to the nitration reaction (a), and further subjecting the resulting mixture without isolating/purifying the resulting compound represented by the formula: ##STR11## PA1 wherein R.sup.1 has the same meaning as defined above, or a salt thereof to the reaction (b) with a compound represented by the formula: EQU Q--CH.sub.2 --NH--R.sup.2 [III] PA1 wherein each symbol has the same meaning as defined above, or a salt thereof, PA1 wherein each symbol has the same meaning as defined above.
Among the starting materials in the above-mentioned method via the isourea derivative, for example, O-methyl-N-nitroisourea (hereinafter, sometimes abbreviated as MNI) or a salt thereof can be usually produced by nitrating O-methylisourea or a salt thereof (Recueil des Travaux Chimiques des Pays-Bas, Vol.81, pp.69, 1962). ##STR5##
In this method, for example, when MNI is obtained by industrially conducting nitration by using nitric acid in sulfuric acid, pouring the reaction mixture into cold water or ice, or a mixture of water and ice after the completion of the reaction, and cooling the mixture to about -15.degree. C. to separate the resulting MNI by filtration, MNI is obtained in a low yield of about 75% at the maximum by only a post-treatment operation such as separation by filtration because of the water-solubility of MNI. Furthermore, the yield is further lowered by increasing the scale of the reaction. The yield increases to about 90% by extracting from a mother liquor for filtration. However, since the solubility of MNI in a usable extraction solvent is not so high, a large amount of an organic solvent is required and, therefore, the operation becomes complicated and is very disadvantageous from an industrial point of view. In the case of using O-methylisourea monomethyl sulfate as a starting material, this compound can be obtained by the reaction between urea and dimethyl sulfuric acid, but this reaction itself proceeds in a yield of only about 60% (Journal of Chemical Society, Vol.1955, pp.3551) and subsequent post-treatment of nitration requires extraction by solvent. Furthermore, MNI corresponds to a dangerous object V under the Jananese Fire Services Act., and has explosive properties.